Neuropathic Pain

Neuropathic Pain

By Lori Montgomery, MD, CCFP

Introduction

There are many definitions of neuropathic (say: noor-uh-PATH-ik) pain. This makes diagnosing and treating it somewhat difficult. The International Association for the Study of Pain defines neuropathic pain as pain that is caused by a problem in the nervous system. This is a very broad definition. In general, it can be split into two types: peripheral and central.

Peripheral neuropathic pain

Peripheral neuropathic pain is pain that happens in the nerves outside the spinal cord, like the ones in your wrist in the case of carpal tunnel syndrome, or in your skin in the case of diabetic neuropathy. This can be a result of:

a systemic (that affects the whole body) problem like diabetes

alcohol abuse

medicine side effect (in which an environment is created that is toxic to nerves)

a more specific problem like a tumour on a nerve

traumatic injury to a nerve

Central neuropathic pain

Central neuropathic pain arises in the brain or spinal cord, such as the pain that happens after a spinal cord injury or a stroke. In both peripheral and central neuropathic pain, the problem is a malfunction (not working how they should) in the nerves themselves. This causes them to transmit pain signals for no useful purpose.

Signs and symptoms

Fibromyalgia affects three to six percent (3 to 6 out of 100) of the population. It varies in severity. Some patients are very mildly affected, while others are very disabled. Some possible symptoms are:

pain which may be burning, shooting, stabbing, or electric shock-like

itching, tingling, or pins and needles sensations

very sensitive skin as if you have a bad sunburn

very sensitive to heat or cold

specific muscle weakness

muscle twitching

sleep disruption (because pain is often worst at night)

Causes

There are more than 100 causes of neuropathic pain. Here are some examples:

alcohol abuse

medicine side effects (for example, certain anti-cancer drugs)

certain vitamin deficiencies

diabetic neuropathy

pressure from a tumour

repetitive stress (like carpal tunnel syndrome)

post-herpetic neuralgia

Diagnostic tests

The tests that are needed will depend on how you describe the pain and what other medical conditions you have.

Blood testsOften, blood tests will be useful to look for things like diabetes, thyroid disease, or vitamin deficiencies.

Monofilament testingThe simplest test is a small filament that your doctor can use in the office to test your sensation. The device applies a constant amount of pressure, so that your doctor can compare your skin sensitivity to that of a person without neuropathy. If you are diabetic, this may be the only other test that needs to be done.

Quantitative sensory testing (QST)Quantitative sensory testing (QST) can be used to make note of changes in your condition over time. This test checks your sensitivity to light touch, pinprick, pressure, vibration, and temperature. It is not often needed to make decisions about treatment, but is helpful in research studies to look at disease progression.

Nerve conduction studies (NCS) or electromyography (EMG)Nerve conduction studies (NCS) or electromyography (EMG): these tests check how well an electrical signal is being transmitted through a nerve, or how well the muscles respond to the nerve signal. These tests are sometimes needed to help narrow down the diagnosis.

Treatment approach

MedicinesThere are a number of medicines that are used to control nerve pain. Some patients may benefit from: